The invention relates to the field of electrode architectures that permit the generation of a multi-polar field, or permit the filtration or the deflection or the focusing of charged particles. More particularly, the invention relates to micro-devices that integrate assemblies of micro-electrodes, also for the purpose of generating a multi-polar field in particular for the filtration or deflection or focusing of charged particles.
The invention finds application notably in the field of mass spectrometry: in effect, the assemblies of electrodes according to the invention can be used in mass spectrometers. The invention therefore also relates to the field of mass spectrometry.
Mass spectrometry is an analysis technique widely used in laboratories and in industry. Using mass spectrometry the nature of constituents of a gas can be determined with a sensitivity better than ppm. To do this, the gas to be analyzed must be at low pressure, in general less than 10xe2x88x924 mbar. This is a limitation for applications where the pressure is greater (10xe2x88x922 mbar) and for which it is then necessary to add pumps and supplementary circuits so as to reduce the pressure in the area where the mass spectrometer is. The creation of a spectrometer of small size (≈1 cm3) would allow one to work under a lower level of vacuum.
In a general way, a mass spectrometer comprises three distinct parts, as illustrated in FIG. 1: an ionization chamber 2, a separator 4 (filter) and an ion detector 6. Many separators are of the quadrupolar type. The theory of uni-polar and quadrupolar mass spectrometers etc is for example described in the book xe2x80x9cTechniques de l""Ingxc3xa9nieurxe2x80x9d, volume P3, P 2615, p. 1-39. The mass filter 4 is the place where, through the set of electromagnetic forces, the ions of different masses are separated. In a quadrupole (an accepted term meaning xe2x80x9ca mass analyzer fitted with a quadrupolar type filterxe2x80x9d), a high frequency electric field is generated between 4 parallel bars 8, 10, 12, 14 such as those shown in FIG. 1. It is assumed that the ions move along the mean direction OZ parallel to the bars.
In a general way, a quadrupolar electric field is such that its amplitude is a linear function of the co-ordinates. The electrical potential is therefore a quadratic form of the co-ordinates. It can be written in the form V=(xcfx86/r2)xc3x97(x2xe2x88x92y2) where r is the distance between the axis OZ and the bars (r is also called the throat radius of the quadrupole) and xcfx86 a constant value of the potential. In order to obtain such a potential distribution, two opposite bars are polarized to +V, while the two others are polarized to xe2x88x92V.
In the case of a quadrupole being used as a filter or a means of focusing or of deflection, the potential V in addition comprises a time dependent component (term in cos xcfx89t) which is used to make the charged particles oscillate. The lines of equipotential, which, at a given moment, correspond to this distribution of potentials (as a function of the potentials applied to the bars) are hyperbolae in the plane XOY. In the ideal case, the cross sections of the bars have this same hyperbolic form. A quadrupolar system with bars 16, 18, 20, 22 of hyperbolic section is illustrated in FIG. 2 and is, for example, described in U.S. Pat. No. 5,373,157.
In the majority of cases, and in order only to use machining that is easy to carry out, the bars have circular cross sections osculating to hyperbolae at their peak; such cross sections 26, 28, 30, 32 are also shown in FIG. 2. A degradation of resolution results from passing from the hyperbola to the circle.
If one wishes to reduce the size of a quadrupolar spectrometer to about 1 cm3, all the dimensions of the filter are affected by this, in particular the radius of the bars, their distance to the center and, of course, their length.
Document WO-96/31901 describes a miniaturized quadrupolar mass spectrometer. This device uses cylindrical beams made from metal coated optical fibers. In such a device, the insulators situated between the cylindrical bars can lead to charge effects which are prejudicial to the operation of the device.
The patent U.S. Pat. No. 5,401,962 describes a miniature quadrupole. In this document, the miniaturization or the reduction in size, originates from the assembly of a plurality of quadrupoles in parallel. This device lacks resolution. Furthermore, its production, even when it uses cylindrical electrodes is rather time consuming.
Document U.S. Pat. No. 4,994,336 describes a control plate for a lithography device. This control plate essentially comprises a semi-conductor substrate in which a window or opening is made to allow the passage of beams of particles. Deflection elements allow the beams to be deflected.
This document also describes methods of producing such a plate. In these methods, the deflection elements are obtained by etching a layer to produce depressions in it that have the shape of deflection elements. The deflection elements are then created along a direction perpendicular to the plane of these layers.
Finally, in this document, the field generated is a uniform field in all directions and in all the space between the flat electrodes. This field is not multi-polar.
The problem posed therefore is that of producing components, notably for their application to mass spectrometry, that allow among other things the miniaturization of the spectrometers.
In particular, the problem is posed of creating assemblies of electrodes which would enable easy production of micro mass spectrometers.
More precisely, a subject of the invention is a micro-device for generating a multi-polar transverse field, comprising n conductive longitudinal micro-beams of polygonal cross section, arranged around a longitudinal axis.
Advantageously, the field is constant along the longitudinal axis.
By a multi-polar field one understands any electrical field, even a mono-polar one. Such a field is not uniform since it is multi-polar or mono-polar.
Consequently, according to the invention, the creation of electric fields on a sub-millimeter scale, and which are derived from potentials which are for example, of the quadrupolar, hexapolar or octopolar type or more generally are N-polar (N greater than 1) can be carried out with electrode structures (also called lenses) in which the electrodes have a cross section of polygonal shape. Such electrodes are compatible with production using micro-electronic or micro-technology techniques and therefore permit the manufacture of miniaturized mass spectrometers.
Another subject of the invention is a micro-device for the filtration or the deflection or the focusing of charged particles, comprising n conductive longitudinal micro-beams, with polygonal cross section, and arranged around a longitudinal axis of propagation of the charged particles.
Another subject of the invention is a micro-device for the filtration, or the deflection or the focusing of charged particles that comprises a micro-device to generate a multi-polar transverse field such as that already described above.
For this, the invention specifies an electrode structure for a micro-device for filtration, or deflection or focusing, which is compatible with production by the techniques of micro-electronics or micro-technology. Electric fields can also be generated for a micro-device for filtration, or deflection or focusing on a sub-millimeter scale.
At present, the electrodes used in a quadrupolar type device, or more generally an N-polar device, have sizes which cannot be reduced below certain dimensions, which limits the lower size of the device. In particular, document U.S. Pat. No. 5,401,962 mentions cylindrical electrodes of a diameter between 0.5 mm and 1 mm, and of a length between about 1 cm and 2 cm. The electrode structure according to the invention allows sub-millimeter devices to be produced (for example with bars whose thickness is a few hundreds of xcexcm) which are able to work at higher pressure (for example about 10xe2x88x922 mbar).
The assembly in parallel of several multi-polar structures according to the invention allows the intensity of the output signal from this same structure to be increased. The production of such a structure proceeds through the production of certain parts of the structure in an individual way, and then through a step of assembling these parts, in parallel.
Means of polarizing the conductive micro-beams can be connected to the multi-polar structures according to the invention. Similarly, means can be linked to them of introducing ions or charged particles along a direction defined by the longitudinal axis or axes. A multi-polar field is linked to each longitudinal axis, all the longitudinal axes being parallel.
According to one particular embodiment, each micro-beam can be produced in a flat substrate and held in the plane of the substrate by support bars.
The micro-device can comprise:
at least first and second sheets made of insulating or semiconductor material
means that allow the sheets to be held parallel at a certain distance from one another,
areas etched into each sheet to define micro-beams in them.
The micro-device comprises for example
first, second and third sheets made of insulating or semiconductor material,
means that allow the first and second sheets to be held parallel at a certain distance from one another,
means that allow the second and third sheets to be held parallel at a certain distance from one another,
areas etched into each sheet defining micro-beams in them.
The means of holding the sheets parallel to one another may, in addition, permit alignment of said sheets in a way that provides the desired multi-polar field. For example, these means are cross members arranged in slots created in the sheets to ensure this alignment.
These structures are totally compatible with collective and extremely precise production (to about xc2x11 xcexcm), which can be implemented using etching techniques and working techniques known in the field of micro-electronics.
Another subject of the invention is a mass spectrometer comprising a micro-device according to the invention, such as that described above, means of introducing ions and means of detection.
Finally, a subject of the invention is a method of producing a micro-device for generating a multi-polar transverse field and in particular a micro-device for the filtration, or the deflection or the focusing of charged particles, comprising the following steps:
etching P substrates made of insulating or semiconductor material in such a manner as to define, in each substrate one or more micro-beams,
coating the micro-beams with metal
assembling P etched substrates in parallel with one another.